The invention concerns a procedure for the display of a measured quantity as a bargraph with the help of a linear array of addressable display elements. The display elements are electrically interconnected as a matrix by connecting together the back electrodes of all elements in each contiguous group of elements and by connecting together the front electrodes of one element from every group. The ON-groups, which are to have all their elements turned on, are addressed together during one time interval and the single mixed group, containing some selected and some unselected elements, is addressed during a second time interval, these intervals alternating at a repetition rate too high to be perceived by the eye.
Such a procedure is known from the German "Offenlegungsschrift" 24 08 062. It is shown therein that all On-groups can be strobed together because they all have the same pattern of selected elements. The mixed group is strobed subsequently, and the OFF-groups are not strobed at all because none of their elements are to be excited. Consequently the duty ratio is about 50%, independent of the resolution of the bargraph display.
It is known, for example from the article "Matrix Addressing of Non-emissive Displays" by A. R. Kmetz in the book Nonemissive Electrooptic Displays, Plenum, New York (1976) pg. 261 ff., that a pseudo-analog bargraph display consisting of a linear arrangement of liquid crystal (LC) elements can be advantageously interconnected electrically into N groups, each containing M adjacent elements, to form an N.times.M matrix. With conventional multiplex addressing of a matrix, the N groups are sequentially strobed while the data corresponding to the desired pattern to be displayed in the strobed group is synchronously presented in parallel to the M segment lines. Since the liquid crystal responds to the effective value of the applied voltage, the voltage discrimination ratio (display quality) G is deleterously influenced by the low duty ratio 1/N which necessarily accompanies a large number of strobed lines: ##EQU1## where G is defined as the quotient of the effective value of the voltage seen by a selected element divided by the effective value of the voltage seen by an unselected element. (For a derivation of this formula, see the aforementioned article, pg. 272, equation 12.) For a given liquid crystal display, the attainable contrast is determined by the voltage discrimination ratio as shown schematically in FIG. 7, pg, 273, of the said article.
However, as indicated above, a bargraph is much simpler to address than a general matrix: there are then only three types of group, and the duty ratio is generally 50%.
Typical waveforms for such an addressing scheme corresponding to the state of the art according to DOS 24 08 062 are shown in FIG. 1. From these pulse diagrams, one can compute the voltage discrimination ratio G between selected and unselected elements of the mixed group: ##EQU2##
In this equation, the terms in numerator and denominator arising from the first and second time intervals in FIG. 1 have purposely been separated and labelled with "on" and "mix". Also in FIG. 1, the amplitude of the drive signal for the segment electrodes is designated with V, while the groups and segments themselves are identified by Gr and Sg, respectively.